NEGATIVE-PRESSURE HYDROCEPHALUS

Two cases of children with closed myelodysplasia, Arnold-Chiari malfor mation, and shunted hydrocephalus who underwent spinal arachnoid cysto pleural shunting are presented. Postoperatively, both patients develop ed craniovertebral symptomatology accompanied by radiologically docume nted ventricular dilation in spite of negative intracranial pressure a nd functional ventriculoperitoneal (VP) shunts. Both patients recovere d after the cystopleural shunts were revised to increase the resistanc e to flow within the system. The authors believe that some communicati on between the arachnoid cyst and the subarachnoid space existed in bo th cases and that the negative pleural pressure was transmitted prefer entially to the spinal and cerebral convexity subarachnoid spaces with relative sparing of the ventricular system. A transmantle pressure gr adient was thereby established, leading to ventricular dilation. The a uthors further suggest that a craniospinal gradient was possibly estab lished as well, leading to craniovertebral symptomatology in the patie nts. Return of flow in the VP shunts was obtained by correcting this i atrogenic transmantle pressure gradient.